Modular hip inserter/positioner

ABSTRACT

A modular hip body/stem inserter comprises a stem inserter and a holder. A proximal body portion of an implant is loaded, or mounted, onto the holder. A distal stem portion of the implant is affixed onto the stem inserter. The modular hip body/stem inserter maintains the proximal body portion and distal stem portion a short distance apart. The stem inserter can be adjusted to control the version of the distal stem, while the holder can be independently adjusted to control the version of the proximal body. Once the version is adjusted to determine a final seating position, the stem inserter portion is removed and the holder is then used to impact the proximal body and distal stem together, thereby locking the implant components together through a taper locking mechanism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/170,129, filed on Jun. 12, 2002, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates generally to arthroplasty and, more particularly,to devices and techniques for positioning a prosthesis.

During the implantation of bowed orthopedic hip implants with fixedneck-bow orientation, there exists a tendency for the implant to rotateor corkscrew as it enters the bow of the femur. This causes anundesirable implant neck orientation otherwise referred to as neckversion (hereafter, simply referred to as “version”). Currentlyavailable bowed modular implants do not address this situation as theyare assembled outside the body with the version set based on trialsprior to implementation. A variety of external assembly devices havebeen developed that set the final implant in the same version as thatdetermined during trial (see, e.g., the Sundial Version Control deviceavailable from Biomet, Inc.).

In addition, the surgeon must estimate the degree of implant rotationand begin the implantation in an undesirable orientation with theexpectation that the implant will be properly orientated at thecompletion of implantation. If optimal implant neck version is notattained, the surgeon must decide whether to leave the implant in anon-optimal orientation and risk possible dislocation, or extract theimplant and re-implant.

SUMMARY OF THE INVENTION

In accordance with an aspect of the invention, a positioning tool forinserting an implant provides independent control of the orientationbetween a first component and a second component of the implant.

In an embodiment of the invention, a positioning tool comprises a firstpiece for engaging a first component of an implant and controlling anorientation thereof; a second piece for engaging a second component ofthe implant; and a third piece for controlling an orientation of theengaged second component such that the engaged first and secondcomponents of the implant do not lock together and wherein the firstpiece and the third piece provide independent version control for thefirst and second components of the implant.

In another embodiment of the invention, a modular hip body/stem inserterwith independent version control of body and stem comprises two parts: astem inserter and holder. The stem inserter also comprises a handle,while the holder comprises a grip. A proximal body portion of an implantis loaded, or mounted, onto the holder. A distal stem portion of theimplant is affixed onto the stem inserter. The modular hip body/steminserter maintains the proximal body portion and distal stem portion ashort distance apart to prevent these implant components from lockingtogether (e.g., via a taper locking mechanism). The stem inserter can beadjusted, e.g., via the handle, to control the version of the distalstem, while the holder can be independently adjusted, e.g., via thegrip, to control the version of the proximal body. Once the version isadjusted to determine a final seating position, the stem inserterportion of the modular hip body/stem inserter is removed and the holderis then used to impact the proximal body and distal stem together,thereby locking the implant components together through the taperlocking mechanism—thus, setting the final implant seating position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustrative embodiment of a hip implant;

FIG. 2 shows an illustrative embodiment of a positioning tool inaccordance with the principles of the invention;

FIGS. 3 and 4 illustrate use of the positioning tool with the hipimplant of FIG. 1; and

FIGS. 5-9 show various component drawings of the elements of thepositioning tool of FIG. 2.

DETAILED DESCRIPTION

The inventive concept is illustrated in the context of a hip body/steminserter used in orthopedic hip implants.

As such, other than the inventive concept, familiarity with hipimplants, and the components used therein, is assumed and not describedfurther herein. (For example, a locking taper for self-locking pieces ofan implant together is well known and not described herein as is a balldetent comprising a spring, ball bearing and associated groove.) Inaddition, it should be appreciated that the inventive concept is notlimited to hip implants and applies to any implant application requiringversion, or orientation, control of different portions of the implant.

An illustrative hip implant 50 is shown in FIG. 1. Hip Implant 50comprises two components: a proximal body 20 and a fluted distal stem 10(only a portion of which is shown in FIG. 1). Proximal body 20 comprisesupright portion 21 for receiving a ball head (not shown), a receptacle23, opening 24 and a tapered portion 22. Distal stem 10 also comprises atapered portion 12. Tapered portions 12 and 22 are interlocking tapersas known in the art such that when distal stem 10 is fully seated intoopening 24 of proximal body 20—distal stem 10 and proximal body 20 arelocked together. Distal stem 10 further comprises female hex end 13 andthreaded female portion 11 (both described further below).

An embodiment of the invention is shown in FIG. 2 with respect to amodular hip body/stem inserter (inserter) 100. The latter is used, inaccordance with one aspect of the invention, to position the hip implant50 into a femur (not shown) such that there is independent control ofthe orientation of the components, or portions, of the implant, hererepresented by proximal body 20 and distal stem 10. In other words,during implantation the surgeon can now independently adjust theorientation of the various parts of the implant.

Inserter 100 comprises a holder (or proximal body impactor) 130, asleeve 140, a shaft 150, a rod (or pin) 160 having a threaded male end161 (rod 160 is hereafter referred to as threaded rod 160), a spring170, and a ball detent 180. (Although not completely shown in FIG. 2,inserter 100 also comprises a handle 105, which is coupled to shaft150.) In the context of this description, the term “stem inserter”refers either to shaft 150 or threaded rod 160, or their combination.(Indeed, in accordance with another aspect of the invention, shaft 150can be easily modified to provide the functions of rod 160.Alternatively, rod 160 could be modified to provide the functions ofshaft 150.)

As illustrated in FIG. 2, threaded rod 160 is disposed within shaft 150,which is also disposed within holder 130. Sleeve 140, which includesspring 170, surrounds holder 130 and is used to position holder 130 onshaft 150 (described further below). (It should be noted that sleeve 140could also be integrated with holder 130.) Ball detent 180 is mounted ondistal end portion 131 of holder 130. It should be observed thatthreaded rod 160, in the direction of distal end portion 131, extendsbeyond shaft 150. In addition, shaft 150 comprises, at the distal end,end 151, which is illustratively hexagon shaped (hereafter, male hex end151). The latter mates with the female hex end 13 of distal stem 10(described further below).

In accordance with one aspect of the invention, the position of shaft150 with respect to holder 130 is adjustable. Shaft 150 furthercomprises, at the proximal end, circular grooves (as represented bygroove 152) and holder 130 comprises, at the proximal end, ball detentpair 132. As can be observed from FIG. 2, if holder 130 is moved up ordown on shaft 150, ball detent pair 132 will periodically engage one ofthe grooves of shaft 150—thus allowing the position of holder 130 withrespect to shaft 150 to be adjusted in finite increments. This enablesinserter 100 to accommodate different size lengths of proximal body 20such that at least a distance d is maintained between the affixedproximal body 20 and affixed distal stem 10. As will become apparentfrom the description below, maintaining at least a separation distance dprevents the proximal body and the distal stem from locking together forallowing independent adjustment of their orientations. It should benoted that other equivalent forms of adjustment may be used such as, butnot limited to, using threaded elements for adjustment of the shaft andholder, wire clips, etc.

As illustrated in FIG. 2, inserter 100 provides for independent versioncontrol about an axis z, via shaft 150, and holder 130. For example,holder 130 can be rotated in direction 1, while shaft 150 can be rotatedin direction 2—thus, an adjustment to the orientation of holder 130 isindependent of any adjustment to the orientation of shaft 150.

Turning now to FIG. 3, a further illustration with hip implant 50 isdescribed. In particular, proximal body 20 is first mounted to holder130 of inserter 100 such that receptacle 23 mates with ball detent 180.The latter provides a secure, temporary, mounting of proximal body 20 toholder 130 of inserter 100. As can be observed from FIG. 3, threadedmale end 161, of threaded rod 160, extends into the opening withinproximal body 20 beyond shaft 150. The portion of FIG. 3 labeled SectionA-A, further illustrates the use of ball detent 180 for temporarilymounting proximal body 20 onto holder 130.

After mounting of proximal body 20 to holder 130 of inserter 100, distalstem 10 is attached to threaded rod 160. This is illustrated in FIG. 4.In particular, distal stem 10 is inserted into opening 24 of proximalbody 20 such that threaded male end 161, of threaded rod 160, engagesfemale threaded portion 11 of distal stem 10. As distal stem 10 isscrewed onto threaded rod 160, female hex end 13 of distal stem 10 isdrawn onto male hex end 151 of shaft 150. Once these hex ends areengaged, the implant components are rigidly held together—without taperportion 22, of proximal body 20, or taper portion 12, of distal stem 10,engaging. This is illustrated in FIG. 4 by the separation distance, d,between distal stem 10 and proximal body 20. Thus, threaded male end 161locks distal stem 10 to inserter 100 and male hex end 151 enables shaft150 to provide rotational control of distal stem 10, via female hex end13. (It should be noted that other forms of attachment can be used toaffix distal stem 10 to rod 160.)

As noted above, and in accordance with one aspect of the invention,inserter 100 initially maintains the taper portions of both proximalbody 20 and distal stem 10 apart by at least a distance d, such thatthey do not lock together. Indeed, and as described above, holder 130can slide, or move, up or down on shaft 150 for providing thisseparation distance for different length proximal bodies.

In this initial arrangement, the orientation of proximal body 20 isadjusted by movement, or rotation, of holder 130, in either directionabout an axis z, e.g., in direction 3 of FIG. 4. (This movement can befacilitated by placement of a grip on holder 130, or alternatively usingthe upright portion 21 of proximal body 20.) Since holder 130 is free tomove around shaft 150—any change to the orientation of proximal body 20via rotation of holder 130 does not affect the orientation of distalstem 10. Similarly, the orientation of distal stem 10 is adjusted byrotation of shaft 150, via handle 105, in either direction about axis z,e.g., in direction 4 of FIG. 4—without effecting the position ofproximal body 20. Thus, inserter 100 provides for independent versioncontrol of proximal body 20 and distal stem 10 as the construct isimpacted (i.e., as the inserter 100 plus implant 50 is inserted into thefemur). As the implant approaches the final seating position (e.g., 5mm-10 mm) continual adjustments can be made to the orientations ofproximal body 20 and distal stem 10. Once in the final seating position,threaded rod 160 and shaft 150 are removed, and holder 130 is then usedto impact the proximal body and distal stem together (e.g., through useof a hammer), thereby locking the implant components together throughthe taper locking mechanism—thus, setting the final implant seatingposition for the assembled implant. Further impacting of holder 130fully seats the assembled implant in the femur.

Turning now to FIGS. 5-9, these figures provide individual views (not toscale) of the various above-described parts of inserter 100 forreference purposes and are not described further herein. FIG. 5 showsproximal body 20; FIG. 6 illustrates holder 130 with locations 133 and134 for ball detent pair 132, and a perspective view 137; FIG. 7 showsshaft 150 with an enlarged view 157 illustrating male hex end 151, and aperspective view 156; FIG. 8 illustrates threaded rod 160; and FIG. 9shows sleeve 140.

Thus, as described above and in accordance with one aspect of theinvention, the modular hip body/stem inserter with independent versioncontrol of body and stem rectifies the problem of neck version controlon modular implants by allowing the proximal body and the distal stem tobe implanted simultaneously while independently controlling the version,or orientation, of the proximal body and distal stem.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. For example, other forms of attachment or lockingmechanisms such as the above-illustrated ball detent, may be used, suchas screws, etc. In addition, the functions provided by rod 160 and shaft150 can be integrated into one component. It is therefore to beunderstood that numerous modifications may be made to the illustrativeembodiments and that other arrangements may be devised without departingfrom the spirit and scope of the present invention as defined by theappended claims.

1. A method for use in performing an implantation of an implant, theimplant comprising a distal body portion and a proximal body portion;the method comprising the steps of: affixing the proximal body portionto a holder of a positioning tool; affixing the distal body portion to astem inserter of the positioning tool; determining a final implantposition with the positioning tool by performing, during implantation,independent adjustments to orientations of the affixed proximal bodyportion and the affixed distal body portion via the holder and the steminserter, respectively.
 2. The method of claim 1 further comprising thesteps of: subsequent to determining the final implant position,separating the stem inserter from the distal body portion of theimplant; and impacting the holder to lock the affixed proximal bodyportion of the implant to the distal body portion of the implant forforming an assembled implant; whereby impacting the holder also drivesthe assembled implant to a final seating position.
 3. The method ofclaim 1 wherein the stem inserter comprises a shaft.
 4. The method ofclaim 1 wherein the stem inserter comprises a rod.
 5. The method ofclaim 1 wherein the stem inserter comprises a shaft and a rod, andwherein the affixing the distal body portion step further includes thestep of using the rod to lock the distal body portion to the shaft, andwherein the determining step includes the step of providing versioncontrol of the locked distal body portion with the shaft.